The pathogenetic mechanisms underlying the different forms of lupus nephritis are being investigated. Detailed analysis of renal biopsy pathology is being conducted on specimens from patients with systemic lupus erythematosus. Biopsies are classified by major category of lupus nephritis, as well as scored on a semiquantitative scale for specific histologic changes indicating the degree of activity and of chronic sclerosing features. The patterns of immune complex deposition and lymphoid cell interaction with different segments of the nephron are being investigated by immunohistologic techniques and electron microscopy. These approaches have facilitated the analysis of the effects of various types of immunosuppressive agents used to halt the progression of lupus nephritis and they will enhance our understanding of the pathogenesis of this diseases.